The present invention relates to a phase receiver Such receivers are described in British patents No. 1530602 U.S. Pat. No. 4,193,034 (Vance), and U.S. application Ser. No. 790,606 (Masterson et al).
In the above mentioned U.S. Pat. No. 4,193,034, we have described a simple radio receiver for FSK signals, used in that case in a radio paging system. RF signals from the aerial are mixed in two high-gain mixers with local oscillator signals which are in phase quadrature and which are at the nominal centre frequency of the input signal. The outputs from the mixers are low-pass filtered so as to extract the difference frequencies with the width of the RF signal. Baseband signals from the filters are amplified in high-gain limiting amplifiers which deliver symmetrically limited outputs at logic level to a D-type flip-flop. One of the outputs is applied to the D input of the flip-flop and the other to its CK input, with the result that the signal appears at the Q output of the flip-flop.
The two channels, each including one of the mixers, in the above arrangement, are referred to as the I and Q baseband channels. In a zero IF radio with such channels, any quadrature error can have a disturbing effect on the fidelity of received or transmitted signals. An object of the invention is to provide a circuit in which such error is reduced or even eliminated.